This invention relates to machines for stiffening portions of flexible material. More particularly it is concerned with providing an improved machine for stiffening selected portions of workpieces such as the toe portions of shoe uppers. While herein shown as well adapted for providing stiffened vamps, it will be understood that features of the invention are of broader utility and have advantage especially where the selected portion to be stiffened is characterized by surface irregularity which, in effect, it is desired to transform and render smooth.
In the prior art a machine having wide acceptance in the shoe industry for applying molten thermoplastic material as a layer adherent to an upper is disclosed in U.S. Pat. No. 3,277,867 issued Oct. 11, 1966 in the names of C. O. Kilham et al. While machines of this type have been successfully employed on different types of work, both lined and unlined, it is found important that a machine have greater versatility in processing certain types of workpieces required to be stiffened, especially those having surface irregularities and/or openings. In the case of vamps, for instance, the irregular surface may occur as a raised seam, either inside or outside, or because of straps or perforations, or simply be uneven surface substances any of which can interfere with application of the thermoplastic in consistantly uniform manner. In some cases the prior means by which, or the prior way in which, the selected area of a workpiece to be coated is presented to an adhesive applicator gives rise to problems for the shoemaker; air, for example, can be trapped between the upper material and the viscous thermoplastic, or the leather may be wiped during application to provide an excess coating in localities that will subsequently harden and consequently prove difficult to last. Improper shoe conforming ultimately leads to uncomfortable wearing.
Some other U.S. patents in the prior art disclosing various machines and different methods of approach pertaining to coating and stiffening flexible sheet material are noted:
U.S. Pat. No. 3,026,573--utilizes injection molding principals.
U.S. Pat. No. 3,316,573--improved shoe stiffening method.
U.S. Pat. No. 3,342,624--a scraper blade moves across a stencil and an opening therein to force coating material into the opening and thus adhere to a shoe part.
U.S. Pat. No. 3,442,743--filling the recess of a mold with thermoplastic, partially hardening the thermoplastic by cooling the mold recess, bringing the mold into alignment with the work, and pressing the mold and work together to secure the molded plastic as a wafer thereon.
U.S. Pat. No. 3,434,170--employs a heat hardenable discrete layer.
U.S. Pat. No. 3,523,814 -- a fluid coating is deposited on a masked work-piece and an applicator is moved across the mask to straddle a gap therein.
U.S. Pat. No. 3,618,151 -- molten polymeric material is flowed onto and around threads of a fabric laid on an area to be stiffened.
In various ways these and other earlier attempts have not always been satisfactory in insuring that irregularity in the material to be stiffened, has been satisfactorily coated with thermoplastic and that interior smoothness in the completed product has been attained.